The present disclosure relates to exhaust systems and more particularly to diesel exhaust gas treatment systems.
Diesel exhaust is typically subject to emissions regulations covering a variety of emission components, including particulate matter and nitrogen oxides (NOx). A variety of exhaust treatment devices have been developed to reduce these emission components. For example, a diesel particulate filter (DPF) can be used to trap diesel particulate matter and oxidize soot, and a selective catalytic reduction (SCR) element can be used to convert the NOx present in exhaust gas into other compounds, such as nitrogen, water, and carbon dioxide. A selective catalytic reduction on filter (SCR+F) element combines SCR and DPF functionality such that NOx reduction and particulate matter filtration and oxidation can occur in a single element.
Typically, diesel exhaust fluid (DEF)—a solution of urea and deionized water—is injected upstream of the SCR element to provide ammonia, which acts as a reducing agent and reacts with the NOx in the presence of the SCR catalyst in accordance with Equation (1):NO+NO2+2NH3→2N2+3H2O  (1)The NOx and ammonia are thus converted into nitrogen and water.